Method of inhibiting corrosion in oil production



United States Patent Ofllice 3,072,192 Patented Jan. 8, 1963 3,072,192METHOD OF INHIBITING CORROSION IN OIL PRODUCTION Hendrik K. Van Poollen,Littleton, Colo., assignor t Marathon Oil Company, a corporation of OhioNo Drawing. Filed Feb. 19, 1959, Ser. No. 794,255 6 Claims. (Cl. 16642)My invention relates to methods for preventing or reducing corrosiveeffects on oil well equipment installed in or associated with producingoil wells.

This invention is useful in various types of producing wells but hasparticular application to treatments utilized in connection with oilwell stimulation. The oil contains ingredients possessing highlycorrosive properties which attack the metallic surfaces in the wellequipment and surface installations through which the oil is conducted,treated and stored.

Among the methods utilized in oil well stimulations is a practice knownas hydraulic fracturing or sand fracturing, in which a fluent body ofsand in graded sizes is pumped or forced into an oil reservoir to rendersuch formation more permeable and to promote flow of oil from thestructure into the production well.

It has been known that corrosion inhibitor compositions, if released inthe structure to flow with the oil, will retard the corrosive action toa considerable degree, and it is beneficial to have the inhibitor inplace when pumping begins.

The present invention represents a departure from prior inhibitionmethods, in utilizing corrosion inhibitors which are in solid form, aresubstantially insoluble in the carrier fluid by which they are conductedinto the formation, and go into solution slowly in the oil production ofthe well, which usually has a substantial water con-tent. The inhibitorcomposition may be water soluble or oil soluble and preferably is onlyslowly soluble in the formation fluids of the oil stream being conductedthrough the well. A suitable composition for this purpose is describedin Rohrback et a1. Patent No. 2,6843 32, and the pellets may be formedto meet size specifications or reduced and sized to meet the sizerequirements of its intended use. A novel method is provided fordistributing such compositions throughout the reservoir structure andcorrosive action is inhibited for a relatively long period due to theslow rate of dissolution.

Accordingly it is an object of my invention to provide a simple,economical and eflicient method of inhibiting corrosion in metallicequipment utilized in oil production.

Another object of this invention is to provide a simple, economical andeflicient method of distributing a corrosion inhibiting composition inan oil producing structure and for retaining such composition in thestructure for a relatively long period.

A further object of the invention is to provide for the distribution ofa corrosion inhibiting composition throughout an oil bearing formationas an adjunct to a charge of material being distributed throughout theformation for other purposes.

A typical procedure according to the present invention is to form solidinhibitor chemicals as pellets which dissolve slowly in formationfluids. These pellets are sized and mixed with propping sand in the samesize ranges until they are uniformly distributed in the sand. Thismixture is utilized as the propping sand of a hydraulic fracturingtreatment and is pumped into cracks away from the well bore. The pelletsare slowly soluble in the formation fluids but supply a suificientinhibiting effect from the outset, and because the rate of dissolutionis so slow, this effect persists for relatively long intervals.

Various compositions may be used as the inhibitor material, as forexample, the class of compositions known as semi-polar organic corrosioninhibitors and inorganic compositions, such as sodium dichromate andsodium nitrite. In preferred practice these inhibitors are mixed with asuitable liquefied inert but slowly soluble material which will congealin the pellet forming stage and can be controlled as to size so that thepellets are produced in the same size range as the propping sand. It isnot necessary to have the inhibitor composition in solution prior tocongealing so long as it disintegrates in the formation fluids andpellets formed of compressed solids also may be employed.

The quantity of pellets utilized in the treatment will vary with theamount of sand being used, the size of the fractured area being filled,and the productivity of the well. In many treatments where aconsiderable quantity of sand is being used, an addition of pellets inan amount approximating one percent by volume of the sand will beadequate under most conditions. Under extreme conditions as much as 10%might be required in such a mixture, but any amount in excess thereofappears to have no actual benefit and only adds to the cost of thetreatment.

The sand-inhibitor mixture is distributed throughout the fractured areaaccording to the usual hydraulic fracturing procedure. As soon as thesand distribution is completed pumping can begin and continues as longas required. The inhibitor commences functioning as pumping begins andcontinues in the same manner for a long interval providing substantiallythe same degree of corrosion control throughout the entire period.

In many instances it may be advantageous to introduce a substantialconcentration of the inhibitor pellets into the formation preceding theintroduction and distribution of propping sand, in order to push theinhibitor far into the formation. In such event, only a lean mixture ofinhibitor in the sand will suflice, as the formation fluids will containdissolved inhibitor on reaching the propping sand.

From the foregoing description it will be apparent that this inventionmay be practiced with a wide selection of chemicals as the inhibitor ofthe treatment, and the quantity of inhibitor used may vary substantiallyaccording to the requirements of a given treatment. Changes andmodifications may be availed of within the spirit and scope of theinvention as set forth in the hereunto appended claims.

I claim:

1. The method of inhibiting corrosion in oil production from hydrocarbonproducing reservoir formations penetrated by a well, which comprisesmixing a corrosion inhibitor composition in solidified pellet form witha propping agent in approximately the same size range, said pelletsbeing substantially insoluble in a carrier fluid and at least slowlysoluble in formation fluids, suspending the mixture of pellets andpropping agent in said carrier fluid, delivering said mixture through awell bore to the bottom of said well, initiating a fracturing of saidformation at the bottom of the well by increasing the pressure on saidcarrier fluid to a degree sufficient to lift the overburden and forcesaid fluid mixture into the formation, whereby it is distributed throughsaid formation outwardly from said well, and withdrawing formationfluids from the formation and through the well to induce a slowdissolution of the pellets by contact with the formation fluids untilthe inhibitor is completely dissolved therein.

2. The method of inhibiting corrosion in oil production from hydrocarbonproducing reservoir formations penetrated by a well, which comprisesmixing a corrosion inhibitor composition in congealed pellet form with apropping agent in approximately the same size range, said pellets beingsubstantially insoluble in a carrier fluid and at least slowly solublein formation fluids, suspending the mixture of pellets and proppingagent in said carrier fluid, delivering said mixture through a well boreto the bottom of said well, initiating a hydraulic fracturing of saidformation at the bottom of the well by increasing the pressure on saidcarrier fluid to a degree suflicient to lift the overburden and forcesaid fluid mixture into the formation, whereby it is distributed throughsaid formation outwardly from said well, and withdrawing formationfluids from the formation and through the well to induce a slowdisolution of the pellets by contact with the formation fluids until theinhibitor is completely dissolved therein.

3. The method of inhibiting corrosion in oil production from hydrocarbonproducing reservoir formations penetrated by a well, which comprisesmixing a water soluble corrosion inhibitor composition in solidifiedpellet form with a propping agent in approximately the same size range,said pellets being substantially insoluble in a carrier fluid and atleast slowly soluble in formation fluids, suspending the mixture ofpellets and propping agent in said carrier fluid, delivering saidmixture through a well bore to the bottom of said well, initiating afracturing of said formation at the bottom of the Well by increasing thepressure on said carrier fluid to a degree suflicient to lift theoverburden and force said fluid mix-ture into the formation, whereby itis distributed through said formation outwardly from said well, andwithdrawing formation fluids from the formation and through the well toinduce a slow dissolution of the pellets by contact with the formationfluids until the inhibitor is completely dissolved therein.

4. The method of inhibiting corrosion in oil production from hydrocarbonproducing reservoir formations penetrated by a well, which comprisesmixing an oil soluble corrosion inhibitor composition in solidifiedpellet form with a propping agent in approximately the same size range,said pellets being substantially insoluble in a carrier fluid and atleast slowly soluble in formation fluids, suspending the mixture ofpellets and propping agent in said carrier fluid, delivering saidmixture through a well bore to the bottom of said well, initiating afracturing of said formation at the bottom of the well by increasing thepressure on said carrier fluid to a degree suflicient to lift theoverburden and force said fluid mixture into the formation, whereby itis distributed through said formation outwardly from said well, andwithdrawing formation fluids from the formation and through the well toinduce a slow dissolution of the pellets by contact with the formationfluids until the inhibitor is completely dissolved therein.

5. A method as defined in claim 1, in which the mixture of pellets andpropping agent is in the proportion of 1 to 10% by volume of pellets insaid agent.

6. A method as defined in claim 1, in which the mixture of pellets andpropping agent is in the proportion of approximately 10% by volume ofpellets in said agent.

References Cited in the file of this patent UNITED STATES PATENTS2,635,698 Rohrback et a1 Apr. 21, 1953 2,684,332 Rohrback et al. July20, 1954 2,818,118 Dixon Dec. 31, 1957 2,877,180 Parks et a1. Mar. 10,1959 2,891,619 Sneary June 23, 1959

1. THE METHOD OF INHIBITING CORROSION IN OIL PRODUCTION FROM HYDROCARBONPRODUCING RESERVOIR FORMATIONS PENETRATED BY A WELL, WHICH COMPRISESMIXING A CORROSION INHIBITOR COMPOSITION IN SOLIDIFIED PELLET FORM WITHA PROPPING AGENT IN APPROXIMATELY THE SAME SIZE RANGE, SAID PELLETSBEING SUBSTANTIALLY INSOLUBLE IN A CARRIER FLUID AND AT LEAST SLOWLYSOLUBLE IN FORMATION FLUIDS, SUSPENDING THE MIXTURE OF PELLETS ANDPROPPING AGENT IN SAID CARRIER FLUID, DELIVERING SAID MIXTURE THROUGH AWELL BORE TO THE BOTTOM OF SAID WELL, INITIATING A FRACTURING OF SAIDFORMATION AT THE BOTTOM OF THE WELL BY INCREASING THE PRESSURE ON SAIDCARRIER FLUID TO A DEGREE SUFFICIENT TO LIFT THE OVERBURDEN AND FORCESAID FLUID MIXTURE INTO THE FORMATION, WHEREBY IT IS DISTRIBUTED THROUGHSAID FORMATION OUTWARDLY FROM SAID WELL, AND WITHDRAWING FORMATIONFLUIDS FROM THE FORMATION AND THROUGH THE WELL TO INDUCE A SLOWDISSOLUTION OF THE PELLETS BY CONTACT WITH THE FORMATION FLUIDS UNTILTHE INHIBITOR IS COMPLETELY DISSOLVED THEREIN.